In the past, a light-emitting device for spotlight illuminating a specific region by emitting light in a specific direction has been used for applications of supplementary lighting, ceiling lighting, or showcase lighting. Recently, a white light emitting diode (white LED) has been used as a light source of a lighting device for spotlight.
Since the white light emitting diode is a semiconductor element with a small size having high power efficiency and emitting light of a bright color, the white light emitting diode has features that it is in no danger of blowout, initial driving characteristics are superior, it is resistant to vibration or repetitive turning-on/off, and the like.
Most of the present white light emitting diodes use fluorescent substance, and such a type of white light emitting diode is generally called bluish yellow pseudo white light emitting diode.
As a planar light source unit for a display, a technique of controlling light distribution characteristics of light emitted from a light emitting diode using a cylinder-like lighting lens was known (for example, see PTL 1). However, when the lighting lens described in Patent Document 1 is used, there is a problem in that it is difficult to handle it due to its heaviness and a problem in that a mold is expensive due to its large size, thereby raising production cost thereof.
To solve these problems, a technique of controlling light distribution characteristics of light emitted from a light emitting diode using plural lighting lenses symmetric about the optical axis of the light emitting diode was known (for example, see PTL 2). In Patent Document 2, plural lighting lenses are arranged on the emission side of the light emitting diode and light emitted from the light emitting diode is concentrated on an illuminated surface side.
FIG. 1 is a diagram illustrating lighting device 1 using lighting lens 10 formed to be symmetric about the optical axis of a light emitting diode in Patent Document 2.
As shown in FIG. 1, lighting device 1 includes rectangular illuminated surface part 11 having illuminated surface 11a and opposing illuminated surface 11b opposing each other and having figures or characters of a signboard described thereon. In lighting device 1, light emitted from a light emitting diode not shown is incident on lighting lens 10, is controlled in its light distribution characteristics by lighting lens 10, and is emitted to illuminated surface part 11.